Recently, in the context of increased direction to environmental protection, electric vehicles (EV), hybrid electric vehicles (HEV) and fuel cell vehicles (FCV) are being developed. As a power source for driving a motor of these vehicles, a repeatedly rechargeable secondary battery is suitable. Particularly, non-aqueous electrolyte secondary batteries such as lithium-ion secondary battery that are expected to have high capacity and high output are attracting public attention.
The non-aqueous electrolyte secondary battery has a positive electrode active material layer containing a positive electrode active material (for example, LiCoO2, LiMnO2, and LiNiO2) which is formed on a surface of a current collector. The non-aqueous electrolyte secondary battery also has a negative electrode active material layer containing a negative electrode active material (for example, lithium metal, carbon materials such as cokes or natural graphite and artificial graphite, metals such as Sn or Si, and oxide materials thereof) which is formed on a surface of a current collector. The non-aqueous electrolyte secondary battery also has an electrolyte layer containing a non-aqueous electrolyte solution or a gel electrolyte, which is provided between the positive electrode active material layer and the negative electrode active material layer to separate the positive electrode active material layer from the negative electrode active material layer. A secondary battery containing a non-aqueous electrolyte solution or a gel electrolyte (gel product obtained as a result of impregnating a non-aqueous electrolyte solution component in a polymer electrolyte) as such an electrolyte is called a “non-aqueous electrolyte secondary battery.” Hereinbelow, when it is described simply as an electrolyte solution, it includes a non-aqueous electrolyte solution component in a gel electrolyte, in addition to a non-aqueous electrolyte solution.
According to the non-aqueous electrolyte secondary battery having the above-mentioned constitution, forming of a coating film on a surface of a negative electrode is promoted and the decomposition reaction of an electrolyte is inhibited during charge and discharge, thus yielding improved cycle characteristics.
However, according to the invention described in Japanese Patent Application No. 2010 080188, decomposition of an electrolyte solution still occurs due to a deviation in resistance in local area within a battery, for a battery (large size cell) with high output (low resistance) and high capacity which is applied for an automobile. Thus, the improvement of the cycle characteristics is not sufficient.